EP3957594A1

EP3957594A1 - Jib crane control system and method for controlling a jib crane

Info

Publication number: EP3957594A1
Application number: EP21191589.7A
Authority: EP
Inventors: Jens Peter Nebsbjerg
Original assignee: HMF Group AS
Current assignee: HMF Group AS
Priority date: 2020-08-18
Filing date: 2021-08-17
Publication date: 2022-02-23
Also published as: DK180746B1; DK202000935A1

Abstract

A method for controlling a crane (2) comprising a jib (4) having a crane tip (16) and a hoist (6) comprising a load connection structure (28), wherein the crane (2) configured to carry a load (14) and comprises:
- one or more of jib actuators (8) arranged to activate the jib (4);
- one or more hoist actuators (10) arranged to activate the hoist (6);
- a control unit (12) configured control the one or more jib actuators (8) and the one or more hoist actuators (10) configured to change the distance (D) between the load connection structure (28) and the crane tip (16). The method comprises the step of providing a command (C_A, C_B) to the control unit (12) to activate the one or more jib actuators (8). The method comprises the following steps:
- determining the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B);
- determining a correcting signal (C_S) suitable for at least partly counteracting the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16);
- activating the one or more hoist actuators (10) by using the determined correcting signal (C_S).

Description

Field of invention

The present invention relates to a control system and a method for controlling a crane comprising an articulated jib and a hoist (cable winch). The invention also relates to a lorry crane (truck-mounted) comprising a control system for controlling a crane comprising an articulated jib and a hoist.

Prior art

When operating the jib of a crane having a jib mounted hoist, the motion of the jib will often affect the hoist in an undesired manner. When the jib is articulated, or parts of the jib are being telescopically displaced relative to each other the distance between a load carried by the hoist and the tip of the jib will change because the length of the uncoiled cable remains constant.
US20050035077A1 discloses a method, by which this undesired effect can be avoided by installing a measuring device arranged and configured to send movement specific feedback to a regulator. Accordingly, the regulation loop can adjust the distance by sending a control signal to the hoist. When applying this regulation loop, one needs to measure the undesired effect continuously and correcting it by using the regulator. This means that the method has a limited speed of correction and requires that accurate measurements are carried out on a continuous basis.
WO2019172415A1 discloses a method and a system for controlling a crane by applying sensor measurements to introduce correction movements when the sensor data reveals that the motion that the crane experienced has an undesired component. This solution is capable of carrying out corrections. However, the corrections can only be carried out after the undesired components of the motion has been realized. Accordingly, it would be desirable to provide a solution, in which this drawback could be avoided.
Thus, there is a need for a method and a control system that reduces or even eliminates the above-mentioned disadvantages of the prior art.

Summary of the invention

The object of the present invention can be achieved by a method as defined in claim 1, a control system as defined in claim 7 and a crane as defined in claim 13. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.
The method according to the invention is a method for controlling a crane comprising a jib having a crane tip and a hoist comprising a load connection structure, wherein the crane is configured to carry a load attached to the load connection structure and comprises:

one or more of jib actuators arranged to activate the jib;
one or more hoist actuators arranged to activate the hoist;
a control unit configured control the one or more jib actuators and the one or more hoist actuators configured to change the distance between the load connection structure and the crane tip,

determining the expected change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command;
determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip;
activating the one or more hoist actuators by using the determined correcting signal.

Hereby, it is possible to provide a method, by which a correction is made before undesired motion actually occurs.
The method suggests application of a feedforward approach. In this manner it is possible to generate a correcting signal and activate the one or more hoist actuators by using the determined correcting signal at that point in time, at which the operator selects and executes a command causing a motion of the jib.
Accordingly, the errors that has to be corrected by the method according to the invention are smaller than the errors needed to be corrected by using prior at systems. At the same time, the method according to the invention is capable of providing a faster and more precise system than the prior art systems.
If the jib is extending, the hoist will release wire at the same time, hereby minimising the errors to be adjusted by the feedback.
The method according to the invention provides a simple, faster and more accurate regulation because it is proactive eliminating majority of the side-effect before it appears instead of allowing it to appear and then react.
The hoist is sometimes known as a cable winch used for lowering and hoisting a load.
In one embodiment, the one or more of jib actuators comprise one or more hydraulic cylinders.
In one embodiment, the one or more hoist actuators comprise one or more motors. In one embodiment, the one or more hoist actuators comprise one or more hydraulically driven motors. In one embodiment, the one or more hoist actuators comprise one or more electrically driven motors.
The control unit configured control the one or more jib actuators and the one or more hoist actuators configured to change the distance between the load and the crane tip. By the term "control" is meant activate and/or deactivate and/or turning on and/or turning off.
Providing a command to the control unit to activate the one or more jib actuators means that the control unit is applied to initiate activation of the one or more jib actuators. This step may comprise application of a regulator connected to the one or more jib actuators.
Determining the expected change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command may be calculated by using the control system and kinematics of the jib. In one embodiment, one or more sensor output may be used to carry out the determination of the change of the distance between the load and the crane tip caused by motion of the jib when executing the command.
Determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip may be done in several ways.
The correcting signal is a feedback in the form of a linear or angular position or derivative thereof (e.g. linear or angular velocity or acceleration). This feedback is sent to the control unit which through a closed loop path regulates the error from an operator-defined setpoint. When a command is provided, the control unit will through the feedforward path calculate a proactive response.
The activation of the one or more hoist actuators by using the determined correcting signal may be carried out in several ways.
In one embodiment, the command is forwarded to a control valve.
In one embodiment, the term "determining" includes that one or more calculations are carried out.
By the phrase "determining the change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command" is meant that the "expected" change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command is determined"
In one embodiment, the control unit comprises a single control device configured to control the one or more jib actuators and the one or more hoist actuators.
In one embodiment, the control unit comprises a first control device configured to control the jib actuators and a second control device configured to control the hoist actuator(s).
By the term "determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip" is meant determining a correcting signal that at reduces the magnitude of the change of the distance between the load connection structure and the crane tip.
In one embodiment, the load connection structure is a hook.
In one embodiment, the load connection structure is an eye (ringshaped structure).
In one embodiment, the crane is a lorry crane (truck-mounted).
It may be an advantage, that the correcting signal is selected in such a manner that activating the one or more hoist actuators by using the determined correcting signal, when not considering the effect of the jib, will cause a hoist induced change of the distance between the load connection structure and the crane tip that is smaller than the jib induced change of the distance between the load connection structure and the crane tip.
This can be expressed as in the following equation: ${ΔD}_{hoist} < {ΔD}_{jib}$
In one embodiment, ΔD_hoist ≤ 0.9 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.8 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.75 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.5 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.4 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.3 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.25 ΔD_jib
Hereby, the method can take into consideration that the speed of the hoist is faster than the speed of the displacement of telescopic extensions of the jib. It provides a simple way to implement the system.
In one embodiment, the command is forwarded to a control valve in a scale from +100 to -100. If the operator of the crane commands +100 straight away this is reached through a first order filter. In this situation it may be advantageous that the correcting signal is decreased by a factor in the rage -0.45 to -0,15. It may be preferred that the correcting signal is decreased by a factor in the range -0.3 to -0.2 such as -0.25. This is a very simple way to execute the correction.
Other ways to calculate the feedforward, apart from a factor, includes a filter, a table and an interval.
In one embodiment, the feedforward is only activated by the extensions of the jib and fly-jib. The feedforward is, however, carried out in such a manner that the feedback does correct all other movements detected in the tip of the crane.
In one embodiment, the method and control system according to the invention comprises a filter is a system that performs mathematical operations to reduce or enhance certain aspects of a signal.
In one embodiment, the filter is a recursive filter.
In one embodiment, the filter is a non-recursive filter.
In one embodiment, the method and control system according to the invention comprises both a recursive and a non-recursive filter.
The filter may include the current value or a combination of the current and previously values. Filters can be simple or complex, of lower or higher order.
In one embodiment, the feedforward calculation is carried out by using a table. This may be accomplished in a manner, in which the table is applied by the control system to look up the current value in the table to see the expected reaction.
In one embodiment, one column in the table would be inputs, whereas another column would be outputs. The control system would therefore for each command be able to select a counter-command from the table.
In one embodiment, the control system carries out the feedforward calculation by using intervals. The idea of intervals allows the system to react different to an input depending on its value. In many systems, a threshold exists. Accordingly, a certain value acts as a threshold. Therefore, the system should react different on each side of the threshold. In one embodiment, there can be multiple intervals.
In one embodiment, the control system carries out the feedforward calculation by using an equation of a line. The equation of a line is another option. Here an input value gets multiplied by a factor before a constant is subtracted or added on. In this way the line can be lifted over a threshold. This is our current implementation of the feedforward: y = ax + b
In one embodiment, the control system carries out the feedforward calculation by using transfer functions. A transfer function is a mathematical expression of an action. It allows the control system to calculate an output if we know the input or vice versa. It transfers the input to an output. In this case the action is the action of a crane's dynamic actions. In order to make the operation in the controller faster this mathematical expression is simplified. It is a balance between accuracy and efficiency.It is possible to calculate an action from its command to the extensions and hence calculate another command to the hoist to counter this action. When a transfer function is modelled a regulator can be found mathematical. It is therefore both used for the feedforward and the feedback.
If several commends are selected simultaneously by the operator, the method comprises the following steps:

determining the expected change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing all commands;
determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip and
activating the one or more hoist actuators by using the determined correcting signal.

The basic idea is to control the hoist in such a manner that, which allow us to keep the distance between the load and the crane tip constant.
It may be beneficial that the method is configured to be used to control a crane that comprises one or more sensors and wherein a sensor output is provided from one or more of the sensors, wherein the sensor output is used by the control unit to determine the change of the distance between the load and the crane tip caused by motion of the jib when executing the command.
It may be an advantage that the one or more sensors are configured and arranged to measure one or more of the following:

a position of structure with respect to a predefined coordinate system;
a velocity of structure with respect to a predefined coordinate system;
an acceleration of structure with respect to a predefined coordinate system;
an angular position of structure with respect to a predefined coordinate system;
an angular velocity of structure with respect to a predefined coordinate system or
an angular acceleration of structure with respect to a predefined coordinate system;

It may be advantageous that the one or more sensors are configured and arranged to measure a position of structure with respect to a predefined coordinate system.
It may be beneficial that the one or more sensors are configured and arranged to measure a velocity of structure with respect to a predefined coordinate system.
It may be advantageous that the one or more sensors are configured and arranged to measure an acceleration of structure with respect to a predefined coordinate system.
It may be beneficial that the one or more sensors are configured and arranged to measure an angular position of structure with respect to a predefined coordinate system.
It may be advantageous that the one or more sensors are configured and arranged to measure an angular velocity of structure with respect to a predefined coordinate system.
It may be beneficial that the one or more sensors are configured and arranged to measure an angular acceleration of structure with respect to a predefined coordinate system.
It may be an advantage that the step of:

determining the expected change of the distance between the load connection structure caused by motion of the jib when executing the command;
determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure;
activating the one or more hoist actuators by using the determined correcting signal,

Hereby, it is possible to provide a method that automatically compensates for the undesired effects of the motion of the jib on a continuous manner.
In one embodiment, the sampling frequency is at least 10 Hz.
In one embodiment, the sampling frequency is at least 20 Hz.
In one embodiment, the sampling frequency is at least 30 Hz.
In one embodiment, the sampling frequency is at least 40 Hz.
In one embodiment, the sampling frequency is at least 50 Hz.
In one embodiment, the sampling frequency is 50 Hz.
In a preferred embodiment, the method comprises the step of applying a regulator to regulate the one or more hoist actuator(s).
In one embodiment, the regulator is in fluid communication with the one or more hoist actuator(s), wherein the one or more hoist actuator(s) are hydraulically driven.
In one embodiment, the regulator is electrically connected with the one or more hoist actuator(s), wherein the one or more hoist actuator(s) are electrically driven.
In one embodiment, the crane comprises a manual hoist control element, wherein the method comprises the following steps

determining the expected change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing all commands;
determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip and
activating the one or more hoist actuators by using the determined correcting signal,

Accordingly, the operator may control the hoist manually if the operator desires. If the operator does not activate the manual hoist control element. This allows (experienced) operators to operate the crane in the same way as they are used to.
In one embodiment, the manual hoist control element is an operating lever.
In one embodiment, the manual hoist control element is a J-stick.
It may be an advantage that the method comprises the step of determining the acceleration of the load and selecting:

a) a first mode if the acceleration of the load is positive;
b) a second mode if the acceleration of the load is negative and
c) a third mode if the acceleration is zero,

Hereby, it is possible to provide a more accurate way of compensating for the undesired effects of the motion of the jib.
In one embodiment, the sampling frequency depends on the mode.
In one embodiment, the acceleration of the load is determined by using a position sensor or an accelerometer arranged on a structure, to which the load is mechanically connected.
In one embodiment, the acceleration of the load is determined by using a position sensor or an accelerometer arranged on the tip of the jib.
In one embodiment, the control system is primarily activated. This means that the system is constantly activated in order to keep the distance between the load connection structure and the crane tip constant.
In one embodiment, the control system is configured to allow the operator to use the hoist to temporarily disable the control system.
In one embodiment, the control system is primarily deactivated. This means that the system is deactivated. In this way the operator can activate control system to maintain the distance between the load connection structure and the crane tip at a fixed level when needed.
In one embodiment, the acceleration of the load is determined by using a position sensor or an accelerometer arranged on a structure, to which the load is mechanically connected.
In one embodiment, the acceleration of the load is determined by using a position sensor or an accelerometer arranged on the tip of the jib.
In one embodiment, the control system is primarily activated. This means that the system is constantly activated in order to keep the distance between the load and the crane tip constant.
In one embodiment, the method is configured to allow the operator to use the hoist to temporarily disable the control system.
In one embodiment, the control system is primarily deactivated.
This means that the system is deactivated. In this way the operator can activate control system to maintain the distance at a fixed level when needed.
The control system according to the invention is a control system for a crane comprising a jib having a crane tip and a hoist comprising a load connection structure, wherein the crane is configured to carry a load attached to the load connection structure and comprises:

one or more of jib actuators arranged to activate the jib;
one or more hoist actuators arranged to activate the hoist;
a control unit configured control (activate and deactivate) the one or more jib actuators and the one or more hoist actuators configured to change the distance between the load connection structure and the crane tip,

Hereby, it is possible to provide a control system enabling that a correction is made before undesired motion actually occurs.
The control system method is based on application of a feedforward approach. In this manner it is possible to generate a correcting signal and activate the one or more hoist actuators by using the determined correcting signal at that point in time, at which the operator selects and executes a command causing a motion of the jib. Accordingly, the errors that has to be corrected when using the invention are smaller than the errors needed to be corrected by using prior at systems. At the same time, the invention provides a faster and more precise system than the prior art systems.
If the jib is extending, the hoist will release wire at the same time, hereby minimising the errors to be adjusted by the feedback.
The control system according to the invention provides a simple, faster and more accurate regulation because it is proactive eliminating majority of the side-effect before it appears instead of allowing it to appear and then react.
The control unit configured control the one or more jib actuators and the one or more hoist actuators configured to change the distance between the load connection structure and the crane tip. By the term "control" is meant activate and/or deactivate and/or turning on and/or turning off.
It may be an advantage, that the control system is configured to select the correcting signal in such a manner that activating the one or more hoist actuators by using the determined correcting signal when not considering the effect of the jib will cause a hoist induced change of the distance between the load connection structure and the crane tip that is smaller than the jib induced change of the distance between the load connection structure and the crane tip.
This can be expressed as: ΔD_hoist < ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.9 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.8 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.75 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.5 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.4 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.3 ΔD_jib
In one embodiment, ΔD_hoist ≤ 0.25 ΔD_jib
Hereby, the control system can take into consideration that the speed of the hoist is faster than the speed of the displacement of telescopic extensions of the jib. It provides a simple way to implement the system.
If several commends are selected simultaneously by the operator, the control system is configured to:

The basic idea is to control the hoist in such a manner that, which allow us to keep the distance between the load connection structure and the crane tip constant.
It may be beneficial that the control system is configured to be used to control a crane that comprises one or more sensors configured to provide sensor output, wherein control unit is configured to apply the sensor output to determine the change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command.
It may be advantageous that the one or more sensors are configured and arranged to measure one or more of the following:

In one embodiment, the control system is configured to:

determining the expected change of the distance between the load connection structure and the crane tip caused by motion of the jib when executing the command;
determining a correcting signal suitable for at least partly counteracting the change of the distance between the load connection structure and the crane tip;
activating the one or more hoist actuators by using the determined correcting signal,

Hereby, it is possible to provide a control system that automatically compensates for the undesired effects of the motion of the jib on a continuous manner.
In one embodiment, the sampling frequency is at least 10 Hz.
In one embodiment, the sampling frequency is at least 20 Hz.
In one embodiment, the sampling frequency is at least 30 Hz.
In one embodiment, the sampling frequency is at least 40 Hz.
In one embodiment, the sampling frequency is at least 50 Hz.
In one embodiment, the sampling frequency is least 50 Hz.
In one embodiment, the crane comprises a manual hoist control element, wherein the control system is configured to:

This allows the operator to control the hoist manually by using the manual hoist control element.
As soon as the operator does not activate the manual hoist control element, the automatic correction of the hoist will be carried out by the control system. The invention allows the operator to operate the crane in the same way as the operator is used to.
In one embodiment, the manual hoist control element is an operating lever.
In one embodiment, the manual hoist control element is a J-stick.
It may be advantageous that the control system is configured to determine the acceleration of the load and select:

In one embodiment, the sampling frequency depends on the mode.
In one embodiment, the control system is primarily activated. The system is constantly activated keeping the distance between the load connection structure and the crane tip constant at all time. When needed the operator will use the hoist to temporarily disable the system and in rare cases disable the system from the controller.
In one embodiment, the control system is primarily deactivated.
The system is deactivated. In this way the operator can activate to maintain the distance between the load connection structure and the crane tip constant when needed from the controller.
The crane according to the invention is a crane comprising a control system according to the invention.
The control system is suitable for operating a lorry crane (truck mounted crane) having at least one boom configured to carry a load. The jib may be a telescopic, or fixed arm that is used to move objects. The jib may be of any suitable type and size.
In one embodiment, the jib is a multi-segment telescopic jib.
In one embodiment, the jib is a fixed arm.
In one embodiment, the jib comprises a pair of sections and hinge members pivotally connecting one section to the other for swinging movement with respect thereto.
The control system is configured to be integrated with the hoist. The control system is activated when the hoist is activated. If the distance between the tip of the crane and the load connection structure be changed it can be done by adjusting with the hoist on the controller. This operation will yield a new setpoint with the new distance and the system will continue to keep this distance until another is chosen by the operator. The invention makes it possible to activate the system when the operator activates the hoist because they work together. If the operator does not want the system active, he can simply use the system to lock a certain position and disable the system afterwards.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1: shows a schematic, perspective view of a crane according to the invention;
Fig. 2: shows a block diagram of a crane according to the invention;
Fig. 3: shows a flowchart illustrating the workflow of a method according to the invention;
Fig. 4: shows a perspective view of a crane according to the invention and
Fig. 5: shows a flowchart illustrating the workflow of a method according to the invention.

Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a crane 2 of the present invention is illustrated in Fig. 1.
Fig. 1 is a schematic, perspective side view of a crane 2 according to the invention. The crane 2 is a truck-mounted crane (lorry crane) that comprises a crane base, onto which a telescopic and articulated jib 4 is mounted. The jib 4 comprises a first telescopic segment S₁ and a second segment S₂ rotatably attached to the first segment S₁. The first telescopic segment S₁ is rotatably attached to the crane base and a jib actuator 8 formed as a hydraulic cylinder 8 is arranged to rotate the first telescopic segment S₁ with respect to the crane base. Another jib actuator 8" is arranged to telescopically extend (lengthen) and shorten the first telescopic segment S₁. The second segment S₂ can be rotated relative to the first segment S₁ by means of a hydraulic cylinder 8'.
The crane 2 comprises a hoist comprising a cable 22 guided by rotatably mounted cable rollers 24. The hoist comprises a hoist actuator 10. The hoist actuator 10 is arranged at the crane base but may be arranged in a different position.
The crane 2 carries a load 14 fixed to a load connection structure (a hook) 28 provided in the distal end of the cable 22. A sensor 18 configured to detect the distance D between the load connection structure 28 and the crane tip 16. When the distance D is changed, the distance between the load 14 and the crane tip 16 will change equally. Accordingly, the sensor can monitor any change distance D between the load connection structure 28 and the crane tip 16 in order to keep the distance D constant. In one embodiment, the sensor is a wire sensor. In one embodiment, the sensor is an optical sensor.
Fig. 2 illustrates a block diagram of a crane according to the invention. The crane 2 comprises a jib 4 having three segments S₁, S₂, S₃ and a crane tip 16. The jib 4 is telescopic and articulated. The jib 4 is mounted on a column 32 placed on a crane base 30.
The crane 2 is equipped with at hoist (cable winch) 6 driven by a hoist actuator 10 arranged to coil and uncoil a cable 22 (indicated with a dotted line). The cable 22 is wound on the hoist 6 and is guided along the jib 4 by means of a plurality of cable rollers 24 to the tip 16 of the jib 4. An attachment structure (for instance a hook like shown in Fig. 1 and Fig. 4), may arranged at the free end of the cable 22 hereby enabling attachment to a load 14.
The direction and magnitude of movements of the cable 22 is measured by a sensor 18 arranged at the roller 24 that is closest to the load 14. The sensor signals are fed to a control unit 12 preferably on a continuous basis.
The jib 4 carries a load 14 attached to a load connection structure 28 arranged in a distance D from the crane tip 16. The crane 2 comprises one or more of jib actuators (not shown) arranged to activate the jib 4 and hereby achieve articulation of the segments S₁, S₂, S₃. Moreover, the crane 2 comprises one or more of jib actuators (not shown) arranged to activate the jib 4 and hereby achieve thrust movements B₁ (jib extension) and/or B₂ (fly-jib extension).
It is indicated that the jib 4 of the crane 1 can perform both articulation movements A₁ (boom movement), A₂ (jib movement), A₃ (fly-jib movement) and also thrust movements B₁ (jib extension), B₂. (fly-jib extension).
The control unit 12 is configured control the one or more jib actuators (see Fig. 1 og Fig. 4) and the hoist actuators 10. The hoist actuator 10 is configured to change the distance D between the load connection structure 28 and the crane tip 16.
The control unit 12 is adapted to maintain distance D relative constant by carrying out a feedforward approach. This means that the control unit 12 configured to ensure that change ΔD of the distance D between the load connection structure 28 and the crane tip 16 remains close to zero (within a predefined range so that the change ΔD of the distance D is smaller than a predefined level). This can be expressed as: $ΔD < L$
wherein L is a predefined allowable level (e.g. 25 cm).
The control system 20 is configured to execute commands. These commands may be inserted by operator of the crane 2 by means og a human-machine interface (HMI) device 34 of suitable type. In Fig. 2 the HMI device 34 is a remote control 34 configured to communicate with the control unit 12.
When the operator 36 by means of the remote control 34 inputs a command C_A (for performing an articulation A₁, A₂, A₃) and/or C_B (for performing a thrust movement B₁, B₂) and/or CH (for activating the hoist actuator 10), the command C_A, C_B will be received by the control unit 12. The control unit 12 will determine the change ΔD_jib of the distance D between the load connection structure 28 and the crane tip 16 caused by motion of the jib 4 when executing the command C_A, C_B.
Hereafter the control unit 12 will determine a correcting signal Cs suitable for at least partly counteracting the change ΔD_jib of the distance D between the load connection structure 28 and the crane tip 16 caused by the motion of the jib 4. The control unit 12 will immediately activate the hoist actuator 10 by using the determined correcting signal Cs. Accordingly, the hoist actuator 10 and the jib actuators are activated simultaneously. In this manner it is possible to achieve that the change ΔD of the distance D between the load connection structure 28 and the crane tip 16 remains close to zero so that the load 14 can be manipulated with the highest possible accuracy by the crane 2.
The control unit 12 is connected to a hydraulic valve 26 that is in fluid communication with the hoist actuator 10 and the jib actuators (not shown). The hydraulic valve 26 is configured to generating actuating signals C'_A, C'_B, C'_S to the hoist actuator 10 and the jib actuators, respectively. The actuating signal C'_A is applied to actuate the jib actuators responsible for articulation A₁, A₂, A₃ of the jib 4. The actuating signal C'_B is applied to actuate the jib actuators responsible for trust movements B₁, B₂ of the jib 4. The actuating signal C's is applied to actuate the hoist actuator 10.
The sensor 18 configured to detect the distance D between the load 14 and the crane tip 16 on the basis of one or more sensor signals X. The sensor signals X may include an angular position θ an, an angular velocity ω, an angular acceleration α, a position y, a velocity v or an acceleration a. Since the sensor 18 monitors the distance D, the control unit 12 has updated information about the distance D. Accordingly, the control unit 12 can determine the most optimum correcting signal Cs for remain a constant distance D between the load connection structure 28 and the crane tip 16.
If the control system 20 is deactivated, it would be possible to raise or lower the load 14 relative to the crane tip 16. In Fig. 2 a lowered load 14 is indicated with a dotted line. When the control system 20 is activated, the control system 20 would use a feedforward approach to keep the distance D constant.
When the operator 36 gives a command C_A and/or C_B the control unit 12 will immediately generate a correcting signal Cs that causes the hoist actuator 12 to counteract the expected change ΔD_jib of the distance D between the load connection structure 28 and the crane tip 16 caused by the motion of the jib 4.
In this way the hydraulic valve 26 only has to correct relative small errors. Accordingly, the control system 20 is capable of providing a faster and more precise regulation of the distance D than the prior art systems.
If for example, the jib 4 is extending, then the hoist actuator 10 will release cable 22 at the same time, leaving a small error to be adjusted by the feedback.
Therefore, the system and method according to the invention, provides a simple, fast and more accurate regulation by proactively eliminating majority of the side-effect before it appears instead of allowing it to appear and then react afterwards.
In one embodiment, the following formula is used or corrections of commands where extensions are included. $Cs = Cs_feedforward + Cs_feedback,$
where Cs is the correcting signal, C_{s_feedforward} is the part of the correcting signal which comes from the feedforward signal and C_{s_feedback} is the part from the feedback loop. In other words, a proactive part that corrects the current movement and a part that correct last cycles error.
If extensions are not part of the command the following equations can be used: $Cs = Cs_feedback$
${ΔD}_{jib} \approx {ΔD}_{feedback} + {ΔD}_{feedforward}$
${ΔD}_{jib} > {ΔD}_{feedforward}$
Fig. 3 illustrates a flowchart illustrating the workflow of a method according to the invention. The method comprises four steps I, II, III, IV.
In the first step I, a command C_A or C_B is selected. The selection may be accomplished by an operator as shown in and explained with reference to Fig. 2. Using a remote control 34 to select the command C_A or C_B is a practical solution. However, in one embodiment, the command C_A or C_B may be inputted directly to the control unit 12.
In the second step II, the expected change of the distance D between the load connection structure 28 and the crane tip 16 caused by executing the command C_A and/or C_B is determined. This may be done by using the control unit 12 to perform a calculation taking into account parameters indicative of the kinematic of the crane jib 4. Such parameters may be measured by sensors arranged at the jib 4.
In the third step III, a correcting signal Cs to be sent to the hoist actuator 10 is determined. The determination may be based on a calculation of the expected change of the distance D between the load 14 and the crane tip 16 caused by motion of the jib 4 when executing the command C_A and/or C_B referred to in the second step II.
In the fourth step IV , the command C_A and/or C_B are executed by the jib actuator(s) 8 and the correcting signal C_S is simultaneously executed by the hoist actuator 10.
This sequence (step I-IV) is repeated in an ongoing manner as long as the control is suitable (as long as the distance D is intended to remain zero or close thereto).
Fig. 4 illustrates a perspective view of a crane 2 according to the invention. The crane 2 is a lorry crane (truck-mounted crane) equipped with a telescopic and articulated jib 4. The jib 4 comprises a first segment S₁ and a second segment S₂ rotatably attached to the first segment S₁. The jib 4 comprises a third telescopic segment S₃ that is rotatably attached to the second segment S₂.
The first segment S₁ is attached to a crane base. A first jib actuator 8 formed as a hydraulic cylinder 8 is arranged to rotate the second segment S₂ with respect to the first segment S₁. A second jib actuator 8' formed as a hydraulic cylinder 8' is arranged to rotate the second segment S₂ with respect to the third segment S₃. A third jib actuator 8" is arranged to telescopically extend (lengthen) and shorten the third telescopic segment S₃. The second segment S₂ can be rotated relative to the first segment S₁ by means of a hydraulic cylinder 8'.
The crane 2 comprises a hoist comprising a cable 22 guided by rotatably mounted cable rollers 24. The hoist comprises a hoist actuator 10. The hoist actuator 10 is arranged at the crane base but may be arranged in a different position.
The crane 2 carries a load 14 fixed to a load connection structure formed as hook 28 attached to the free end of the cable 22. A sensor adapted to detect the distance between the load connection structure 28 and the crane tip is arranged at the crane tip. Accordingly, the sensor can monitor any change distance D between the load connection structure 28 and the crane tip.
Fig. 5 illustrates a flowchart illustrating the workflow of a method according to the invention. The method comprises five steps V, VI, VII, IIX, XI.
In the first step V, it is determined if the manual hoist control element is activated. The manual hoist control element may for example be an operating lever or a J-stick.
If the manual hoist control element is activated nor correcting signal is executed by the hoist actuator 10 as indicated in step X. This means that the operator operates the hoist manually. This manual control mode continues as long as the operator activates the manual hoist control element.
If, however, the manual hoist control element is not active (this is the case when the operator does not activate the manual hoist control element). The steps VI, VII, IIX and IX corresponding to the steps I, II, III, IV (shown in and explained with reference to Fig. 3), respectively, are carried out.
This means that the operator can use the manual hoist control element to control the hoist when desired. Whenever, the operator does not use the manual hoist control element to control the hoist, however, the control system will automatically carry out the correction scheme as indicated in the steps VI, VII, IIX and IX.

List of reference numerals

2: Crane
4: Jib
6: Hoist
8, 8', 8": Jib actuator
10: Hoist actuator
12: Control unit
14: Load
16: Crane tip
18: Sensor
20: Control system
22: Lifting cable
24: Cable roller
26: Hydraulic valve
28: Load connection structure (e.g. hook)
30: Crane base
32: Column
34: Human-machine interface
36: Operator
D: Distance
ΔD: Change of distance
ΔDjib: Change of distance caused by jib activity
ΔDhoist: Change of distance caused by hoist activity
ΔDfeedforward: Change of distance
ΔDfeedback: Change of distance
CA, CB: Command
Cs: Correcting signal
Cs_feedforward: Signal
CS_feedback: Signal
C'A, C'B, CH: Actuating signal
θ: Angular position
ω: Angular velocity
α: Angular acceleration
y: Position
v: Velocity
a: Acceleration
f: Sampling frequency
A1, A2, A3: Articulation
B1, B2: Trust movement
I, II, III, IV: Step
S1, S2, S3: Segment
X: Sensor signal (sensor output)

Claims

A method for controlling a crane (2) comprising a jib (4) having a crane tip (16) and a hoist (6) comprising a load connection structure (28), wherein the crane (2) is configured to carry a load (14) attached to the load connection structure (28) and comprises:
- one or more of jib actuators (8, 8', 8") arranged to activate the jib (4);

- one or more hoist actuators (10) arranged to activate the hoist (6);

- a control unit (12) configured control the one or more jib actuators (8) and the one or more hoist actuators (10) configured to change the distance (D) between the load connection structure (28) and the crane tip (16),
wherein the method comprises the step of providing a command (C_A, C_B) to the control unit (12) to activate the one or more jib actuators (8, 8', 8"), characterised in that the method comprises the following steps:
- determining the expected change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B);

- determining a correcting signal (Cs) suitable for at least partly counteracting the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16);

- activating the one or more hoist actuators (10) by using the determined correcting signal (Cs).
A method according to claim 1, characterised in that the correcting signal (C_S) is selected in such a manner that activating the one or more hoist actuators (10) by using the determined correcting signal (C_S) when not considering the effect of the jib (4) will cause a hoist induced change (ΔD_hoist) of the distance (D) between the load connection structure (28) and the crane tip (16) that is smaller than the jib induced change (ΔD_jib) of the distance (D) between the load connection structure (28).
A method according to claim 1 or 2, characterised in that the method is configured to be used to control a crane (2) that comprises one or more sensors (18) and wherein a sensor output (X) is provided from one or more of the sensors (18), wherein the sensor output (X) is used by the control unit (12) to determine the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B).
A method according to claim 3, characterised in that the one or more sensors (18) are configured and arranged to measure one or more of the following:
- a position (y) of structure with respect to a predefined coordinate system;

- a velocity (v) of structure with respect to a predefined coordinate system;

- an acceleration (a) of structure with respect to a predefined coordinate system;

- an angular position (θ) of structure with respect to a predefined coordinate system;

- an angular velocity (ω) of structure with respect to a predefined coordinate system or

- an angular acceleration (α) of structure with respect to a predefined coordinate system;
A method according to one of the preceding claims, characterised in that the step of:
- determining the expected change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B);

- determining a correcting signal (Cs) suitable for at least partly counteracting the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16);

- activating the one or more hoist actuators (10) by using the determined correcting signal (Cs),
are carried out on a continuous basis, wherein the sampling frequency (f) of the determination of the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B) is at least 5 Hz.
A method according to one of the preceding claims, characterised in that the crane (2) comprises a manual hoist control element, wherein the method comprises the step of operating the crane (2) as defined in claim 1 when the manual hoist control element is not activated, wherein no automatic correction signal is executed by the hoist actuator (10) when the manual hoist control element is activated.
A control system (20) for a crane (2) comprising a jib (4) having a crane tip (16) and being provided with a hoist (6) comprising a load connection structure (28), wherein the crane (2) is configured to carry a load (14) attached to the load connection structure (28) and comprises:
- one or more of jib actuators (8, 8', 8") arranged to activate the jib (4);

- one or more hoist actuators (10) arranged to activate the hoist (6);

- a control unit (12) configured control the one or more jib actuators (8) and the one or more hoist actuators (10) configured to change the distance (D) between the load connection structure (28) and the crane tip (16),
wherein the control system (20) comprises a control unit (12) configured to activate the one or more jib actuators (8, 8', 8"), characterised in that the control system (20) is configured to:
- determining the expected change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B);

- determining a correcting signal (Cs) suitable for at least partly counteracting the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16);

- activating the one or more hoist actuators (10) by using the determined correcting signal (S).
A control system (20) according to claim 7, characterised in that the control system (20) is configured to select the correcting signal (Cs) in such a manner that activating the one or more hoist actuators (10) by using the determined correcting signal (C_S) when not considering the effect of the jib (4) will cause a hoist induced change (ΔD_hoist) of the distance (D) between the load connection structure (28) and the crane tip (16) that is smaller than the jib induced change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16).
A control system (20) according to claim 7 or 8, characterised in that the control system (20) is configured to be used to control a crane (2) that comprises one or more sensors (18) configured to provide sensor output (θ, ω, α, y, v, a), wherein control unit (12) is configured to apply the sensor output (α, ω, y, v) to determine the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B).
A control system (20) according to claim 9, characterised in that the one or more sensors (18) are configured and arranged to measure one or more of the following:
- a position (y) of structure with respect to a predefined coordinate system;

- a velocity (v) of structure with respect to a predefined coordinate system;

- an acceleration (a) of structure with respect to a predefined coordinate system;

- an angular position (θ) of structure with respect to a predefined coordinate system;

- an angular velocity (ω) of structure with respect to a predefined coordinate system or

- an angular acceleration (α) of structure with respect to a predefined coordinate system;
A control system (20) according to one of the preceding claims 7-10, characterised in that the control system (20) is configured to:
- determining the expected change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B);

- determining a correcting signal (Cs) suitable for at least partly counteracting the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16);

- activating the one or more hoist actuators (10) by using the determined correcting signal (Cs),
on a continuous basis, wherein the sampling frequency (f) of the determination of the change (ΔD_jib) of the distance (D) between the load connection structure (28) and the crane tip (16) caused by motion of the jib (4) when executing the command (C_A, C_B) is at least 5 Hz.
A control system (20) according to one of the preceding claims 7-11, characterised in that the crane (2) comprises a manual hoist control element, wherein the control system (20) is configured to operating the crane (2) as defined in claim 7 when the manual hoist activator control element is not activated, wherein the control system (20) is configured to operate the crane (2) in a manner, in which no automatic correction signal is executed by the hoist actuator (10) when the manual hoist control element is activated (by the user).
A crane (2) comprising a control system (20) according to one of the claims 7-12.